Process for producing fluorocarboxylic anhydride

ABSTRACT

A method of producing (R f CO) 2 O by reacting R f COCl with M m CO 3  can efficiently synthesize a fluorocarboxylic anhydride in a one-step reaction, 
     wherein R f  is a saturated hydrocarbon group having 1 to 20 carbon atoms, which optionally has an oxygen atom, in which all or part of hydrogen atoms are substituted with a fluorine atom, or a fluorine atom and another halogen atom, M is an alkali metal or an alkali earth metal, m is 2 when M is the alkali metal, or 1 when M is the alkali earth metal.

This application is the national phase under 35 U.S.C. § 371 of PCT International Application No. PCT/JP00/08765 which has an International filing date of Dec. 12, 2000, which designated the United States of America.

TECHNICAL FIELD

The present invention relates to a method of producing a fluorocarboxylic anhydride by using R_(f)COCl as a raw material.

RELATED ART

A method of synthesizing a fluorocarboxylic anhydride which is used as an agent for introducing R_(f)CO and a dehydrating agent is known. For example, in the case of (CF₃CO)₂O, known are the following four synthesis procedures:

-   1. CF₃CO₂H+P₂O₅→(CF₃CO)₂O+polyphosphoric acid (Bourne E. J., Stacey     M., Tatlow J. C., Tedder J. M., J.Chem.Soc., 1949, 2976) -   2. (CHCl₂CO)₂O+2CF₃CO₂H→(CF₃CO)₂O+2CHCl₂CO₂H

(JP-A-61-33139)

-   3. CF₃COCl+ZnO, CuO, CdO→(CF₃CO)₂O+ZnCl₂, CUCl₂, CdCl₂

(JP-B-46-6888)

-   4. CF₃COCl+CF₃CO₂M→(CF₃CO)₂O+MCl(M=Na, K, Zn_(1/2), Ba_(1/2))

(JP-B-45-38523)

In Synthesis Procedure 1, P₂O₅ which is a hydrating agent can usually dehydrate three molecules of water, but P₂O₅ performs the ability of dehydrating only one molecule of water in the case of dehydrating perfluorocarboxylic acid. Therefore, a large amount of P₂O₅ is necessary and the reaction is quitted with having the remaining dehydrogenation ability. It is difficult to post-treating P₂O₅ after the reaction.

Synthesis Procedure 2 needs an excess amount of CF₃CO₂H, and CF₃CO₂H has a small conversion ratio. In order to convert by-produced CHCl₂CO₂H to an anhydride, a dehydrating agent (for example, P₂O₅) is additionally necessary and a waste treatment of the produced H₃PO₄ is also necessary.

Synthesis Procedure 3 needs an excess amount of CF₃COCl and needs the cost for treatment of by-produced ZnCl₂ and the like.

Synthesis Procedure 4 has many steps, since a carboxylate salt, CF₃CO₂M is provisionally reacted with CF₃CO₂H and an alkali salt. In addition, CF₃CO₂M has high deliquescence and it is difficult to control a water content.

SUMMARY OF INVENTION

An object of the present invention to provide a method of synthesizing (R_(f)CO)₂O from R_(f)COCl without the above defects, for example, without using a plural of steps.

We intensively studied to solve the above problems and discovered that the use of R_(f)COCl and a low-cost carbonate salt of alkali metal or alkali earth metal can efficiently produce (R_(f)CO)₂O.

The present invention provides a method of producing (R_(f)CO)₂O by reacting R_(f)COCl with M_(m)CO₃,

wherein R_(f) is a saturated hydrocarbon group having 1 to 20 carbon atoms, which optionally has an oxygen atom, in which all or part of hydrogen atoms are substituted with a fluorine atom, or a fluorine atom and another halogen atom, M is an alkali metal or an alkali earth metal, m is 2 when M is the alkali metal, or 1 when M is the alkali earth metal.

DETAILED EXPLANATION OF INVENTION

The method of preparing (R_(f)CO)₂O by the reaction between R_(f)COCl and M_(m)CO₃ is represented by the reaction formula: 2R_(f)COCl+M_(m)CO₃→(R_(f)CO)₂O+mMCl_(2/m)+CO₂ wherein R_(f) is a saturated hydrocarbon group having 1 to 20 carbon atoms, which optionally has an oxygen atom, in which all or part of hydrogen atoms are substituted with a fluorine atom, or a fluorine atom and another halogen atom, M is an alkali metal or an alkali earth metal, m is 2 when M is the alkali metal, or 1 when M is the alkali earth metal.

R_(f) is a saturated hydrocarbon group having 1 to 20 carbon atoms, particularly 1 to 10 carbon atoms, which optionally has an oxygen atom, in which all or part of hydrogen atoms are substituted with a fluorine atom, or a fluorine atom and another halogen atom. R_(f) has at least one fluorine-containing atom.

R_(f) may be:

-   X(C_(m)X_(2m))_(n)—, -   X(C_(m)X_(2m))_(n)(C_(s)X_(2s))_(t)— -   X(C_(m)X_(2m)O)_(n)—, or -   X(C_(m)X_(2m)O)_(n)(C_(s)X_(2s))_(t)—     wherein each X is a halogen atom or a hydrogen atom, at least one X     is a fluorine atom, n is an integer of 1 to 10, m is an integer of 1     to 5, s is an integer of 1 to 5, and t is an integer of 1 to 10.

R_(f) may be a perfluoroalkyl group (F(CF₂)_(i)—), and may be liner or branched. i is from 1 to 20, for example, from 1 to 10, preferably from 1 to 7.

Specific examples of R_(f)COCl include:

-   HCF₂COCl -   CF₃COCl -   CF₃CF₂COCl -   CF₃CF₂CF₂COCl -   H(CF₂CF₂)_(n)COCl -   Cl(CF₂CFCl)_(n)CF₂COCl -   CF₃CF₂O(CF₂CF₂CF₂O)_(n)CF₂CF₂COCl and -   CF₃CF₂CF₂OCF(CF₃)COCl     wherein n is from 1 to 10.

M is an alkali metal or an alkali earth metal, and is preferably Li, Na, K and/or Ca.

A yield of (R_(f)CO)₂O is dependent on the used carbonate salt. The stabler a salt of MCl_(2/m). produced at the reaction is, the higher the yield is. The carbonate salt is preferably K₂CO₃, CaCO₃, Na₂CO₃ and Li₂CO₃.

A molar ratio of R_(f)COCl to the carbonate salt is preferably at least 2.

A reaction temperature is preferably from 0° C. to 150° C., for example, from 10° C. to 50° C. If the reaction temperature is high, the product undesirably begins to decompose.

A reaction pressure is not specifically limited and may be from atmospheric pressure to 2 MPa (gauge pressure). When the reaction pressure is high, the raw material, R_(f)COCl is liquefied so that the contact between the reactants is improved so as to accelerate the reaction.

A reaction time is not specifically limited and may be from 20 minutes to 600 minutes, for example, from 120 minutes to 240 minutes.

In the present invention, (R_(f)CO)₂O can be prepared in a one-step reaction with good yield by using R_(f)COCl and the low-cost carbonate salt of alkali metal or alkali earth metal.

A solvent may not be used in the present reaction. However, since the reaction is exothemic, the solvent may be used for the purpose of removing the heat.

A polar solvent and a nonpolar solvent can be used as the solvent.

Examples of the polar solvent include acetonitrile (CH₃CN), CH₃O(CH₂CH₂O)_(n)CH₃ (n=0˜4), nitrobenzene (C₆H₅NO₂), dimethylformamide (DMF), dimethylsulfoxide (DMSO) and acetone.

Examples of the nonpolar solvent include a fluorine-containing solvent (for example, C₄F₆Cl₄ and C₆F₉Cl₅), CCl₄ and C_(n)H_(2n+2) (n=5 to 10).

When the polar solvent is used, a carbonate gas is produced and then an anhydride is produced. When the nonpolar solvent is used, the carbonate gas may be produced simultaneously with production of the anhydride. The polar solvent may give easier treatment of the produced carbonate gas, and the easiness of the treatment is dependent on a reaction apparatus.

For example, when R_(f)COCl is CF₃COCl and the carbonate salt is Na₂CO₃, a whole reaction is: 2CF₃COCl+Na₂CO₃→(CF₃CO)₂O+2NaCl+CO₂, which whole reaction proceeds in two-step reactions: CF₃COCl+Na₂CO₃→CF₃COONa+NaCl+CO₂ and CF₃COONa+CF₃COCl→(CF₃CO)₂O+NaCl. The reaction can be proceeded in a one-step reaction, or the reaction can be divided into two steps as in the above. In this case, the drawing of the carbonate gas is advantageous in view point of an equipment (pressure resistance), since the pressure of the reactor does not become large. Particularly, when the polar solvent is used, the above two-step reaction can be quantatively proceeded. That is, when the CF₃COCl raw material which is corresponding to the first step reaction (stoichemical amount of raw material) is introduced, the reaction stops after the first step reaction without the proceeding of the second step. When carbonate gas is released during the reaction, the release can be advantageously conducted without loss of the raw material. The second step reaction may be conducted at a temperature of at most 70° C., preferably at most 50° C., more preferably at most 30° C., since a reverse reaction of the second step reaction might proceed. Accordingly, these defined temperatures are preferable also when the object product is recovered. A distillation recovery is conducted preferably at a reduced pressure.

(R_(f)CO)₂O obtained according to the present invention can be used as an agent for introducing R_(f)CO and a dehydrating agent.

PREDERRED EMBODIMENTS OF INVENTION

Examples are shown hereinafter to illustrate the present invention.

EXAMPLE 1

Into a 250 mL stainless steel autoclave, charged was 9.3 g (87.7 mmol) of dried Na₂CO₃. Then, the autoclave was cooled in dry ice/acetone, and 23.2 g (175.4 mmol) of CF₃COCl was charged and reacted with stirring. A reaction temperature was from 21.4° C. to 31.7° C. and a reaction time was 80 minutes. A maximum pressure was 0.8 MPa. A yield was 89.7% according to ¹⁹F-NMR (Conversion: 89.7% and Selectivity: 100%).

EXAMPLE 2

Into 250 mL stainless steel autoclave, charged was 8.2 g (77.4 mmol) of dried Na₂CO₃. Then, 50 mL of C₄F₆Cl₄ as a solvent was charged. The autoclave was cooled in dry ice/acetone, and 21.7 g (163.8 mmol) of CF₃COCl was charged and reacted with stirring. A reaction temperature was from 25.0° C. to 26.1° C. and a reaction time was 275 minutes. A maximum pressure was 0.37 MPa. A yield was 87.4% according to ¹⁹F-NMR (Conversion: 87.4% and Selectivity: 100%).

EXAMPLE 3

Into 250 mL stainless steel autoclave, charged was 9.3 g (87.7 mmol) of dried Na₂CO₃. Then, 50 mL of C₄F₆Cl₄ as a solvent was charged. Then, the autoclave was cooled in dry ice/acetone, and 25.2 g (190.2 mmol) of CF₃COCl was charged and reacted with stirring. A reaction temperature was from 71.1° C. to 77.6° C. and a reaction time was 222 minutes. A maximum pressure was 0.83 MPa. A yield was 85.2% according to ¹⁹F-NMR (Conversion: 85.2% and Selectivity: 100%).

EXAMPLE 4

Into 250 mL stainless steel autoclave, charged was 9.4 g (88.7 mmol) of dried Na₂CO₃. Then, 50 mL of C₆H₁₄ as a solvent was charged. Then, the autoclave was cooled in dry ice/acetone, and 24.0 g (181.1 mmol) of CF₃COCl was charged and reacted with stirring. A reaction temperature was from 22.1° C. to 25.0° C. and a reaction time was 231 minutes. A maximum pressure was 0.53 MPa. A yield was larger than 84.5% according to ¹⁹F-NMR (Conversion: >84.5% and Selectivity: 100%).

EXAMPLE 5

Into 250 mL stainless steel autoclave, charged was 9.6 g (90.6 mmol) of dried Na₂CO₃. Then, 50 mL of CH₃CN as a solvent was charged. Then, the autoclave was cooled in dry ice/acetone, and 24.7 g (186.4 mmol) of CF₃COCl was charged and reacted with stirring. A reaction temperature was from 21.6° C. to 60.0° C. and a reaction time was 175 minutes. A maximum pressure was 0.36 MPa. A yield was 74.0% according to ¹⁹F-NMR (Conversion: >74.0% and Selectivity: 100%).

EXAMPLE 6 (TWO-STEP REACTION)

Into a 500 mL stainless steel autoclave equipped with a fractionating column, charged were 200 g (1.89 mol) of Na₂CO₃ and 335 mL (260 g) of CH₃CN. Then, a system was replaced with vacuum, and the reaction was conducted in two steps.

In a first step, the autoclave was cooled in an ice bath, and each portion of CF₃COCl (29 g) was charged and the charge was repeated (nine portions in total were charged) to conduct the reaction under the conditions of a charge time: 3 to 6 min., a reaction time after the charge: 10 min., and a CO₂blow time after the reaction: 5 min. Total amount of CF₃COCl used for the reaction was finally 254 g (1.92 mol). After the first step reaction, 300 mL of CH₃CN was released at a reduced pressure of 400 mmHg.

After the release of CH₃CN, 259 g (1.96 mol) of CF₃COCl was charged to conduct the second step reaction at a temperature of at most 40° C. A temperature at the completion of the reaction was 27° C. After the completion of the second step reaction, the distillation was conducted at a reduced pressure of 400 mmHg to recover 332 g (1.54 mol) of (CF₃CO)₂O. A yield was 81.6% according to ¹⁹F-NMR (Conversion: 81.6% and Selectivity: 100%).

EFFECT OF INVENTION

According to the present invention, (R_(f)CO)₂O can be produced by using R_(f)COCl as a raw material in a one-step reaction. 

1. A method of producing (R_(f)CO)₂O by reacting R_(f)COCl with M_(m)CO₃, wherein R_(f) is a saturated hydrocarbon group having 1 to 20 carbon atoms, which optionally has an oxygen atom, in which all or part of hydrogen atoms are substituted with a fluorine atom, or a fluorine atom and another halogen atom, M is an alkali metal or an alkali earth metal, m is 2 when M is the alkali metal, or 1 when M is the alkali earth metal.
 2. The method according to claim 1, wherein a reaction temperature is from 0° C. to 150° C.
 3. The method according to claim 1, wherein a reaction pressure is from atmospheric pressure to 2 MPa (gauge pressure).
 4. The method according to claim 1, 2 or 3, wherein a polar solvent is used as a solvent.
 5. The method according to claim 1, wherein the reaction is divided into two steps, and carbonate gas is drawn in a first step reaction.
 6. The method according to claim 1, wherein produced (RfCO₂)O is recovered by distillation under a reduced pressure. 